OpenGL comes straight from my distro no modding involved.
Requirements are for Windows users - DirectX being a proprietary windows package (note the little icon,
). That is only implied in the OP but anyone with a little knowledge would understand. As a Linux user I am unable to install DX (barring going a roundabout route using Wine but then I would need to run the windows build of the game).
The Unreal Engine does not require DX instead it has its own abstraction layer above this. See for example
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As far as I understand RHI (by default) calls the DX api on windows and the OpenGL one on Linux. (There may be configurable options at build time, at a guess.)
No bullshit and no modded OpenGL. You really don't know what you are talking about.